Comet Holmes - October 2007

This periodic comet normally sits around 17th magnitude even on good returns. But around once a century it seems to undergo a massive outburst. This happened on Oct 24, and the comet increased in brightness by a factor of 1 million (!), going from too faint to see in any Cabrillo telescope all the way up to being as bright as any star in Perseus. Our Astro 9 class headed up to the horticulture hill and took photos. Since the comet itself was just a bright, slightly out of focus yellow star, we had to get imaginative to make a compelling picture... enjoy! The first two photos were submitted to and I hope will be published for everyone to enjoy. Thanks, guys, for your modelling and beaming efforts!

Oct 24 7:50pm "Don't Cross the Beams!". Two laser pointers show Comet Holmes while students (and LIA Karl w/ binoc's) look on.

Oct 24 8:00pm. Dimage A1 at ISO 400, 10 sec at f/4.5. Jay expertly painted a circle around the comet with his 50 mw laser pointer

Oct 24. Allen Ginzburg took this shot through his 10" LX200. A 11x1sec + 6x2sec stack in Registax, and processed in Photoshop

Oct 27 - After a halloween party, the sky cleared and I stopped by Cabrillo Observatory to try and photograph the comet with the Meade 8" f/4 LXD75 + GM8 mount + ST2000XCM camera. I set up the gear so as to block the nearby full moon with the observatory building. The comet was slightly fainter than Algol, m=2.4 in my judgement.But it had grown considerably over the past few days, and showed a distinct head/coma in 10x70 binoc's. I was so intent on photography that I never did stick in an eyepiece and actually look at it with my eye. Big mistake! How could I properly Photoshop the result? But I think the result below is a reasonable rendition. Whatever happened to this poor comet, the gas atoms are clearly streaming away in a perfectly sphericical way. The dust grains are heavier and moving more slowly and remain in a tighter circle. The comet light is hugely dominated by dust reflection. I'd guess this is a very old comet whose gas has been hidden under a thick crust of crud for a long time, and hence it's been at 18th magnitude till something hit it or it decided to break off a good bit of crust 3 days ago. I did 5x2-minute exposures, which showed the green coma well, but the dust part was overexposed. So I did a 33 second shot as well, and 'curve'd it in Photoshop to even better bring out the inner double head structure. Then used Photoshop's "high dynamic range" command to merge the 3. The results can no doubt be improved - I need more practice with the HDR command - but the final result does show the full range. The frame below is about a degree across.

Oct 27 11:50pm approximately. 5x2min stack (11:53pm-12:06am)(sRGB+gamma) + 33sec (at 11:43pm)(DDP) + 'curved' 33sec version, merged w/ HDR in PS-CS2, then levels, smart-sharpened, Astronomy tools 'space noise reduction', 'make stars smaller', cropped. No hue/saturation adjustment; these are the colors that emerged from the processing.

Oct 30 ~10pm. with 8" f/4 at Cabrillo. LXD75. 9x30sec stack (sRGB+gamma). levels, 3x 'make stars smaller', 'space noise reduction', no cropping

Nov 3 - A photo trip with Jessica G to Coast Road Reservoir for a night of photography, especially Comet Holmes. Check this page for the photos as processed by Jessica. I did my own first-look processing too...

Comet Holmes Nov 4 @10:16pm PDT. A 3x5min stack. No range adjustment within CCDOPS. sRGB+gamma color processing. Photoshop CS2+Astronomy Tools: 'make stars smaller', 2x 'space noise reduction', severe "levels" to bring gray almost to the lowest levels to bring out faintest isophots. NO color saturation adjustment or cropping. The C2 molecular emission green cloud is still expanding faster than the dust cloud, and a very forshortened tail is beginning to be visible, in blue (gas) and brown (dust) at upper right.

Comet Holmes Nov 4 9:47pm PDT. A 10x5-sec set of exposures stacked. The trick here was to adjust the "range" while still within CCDOPS before rendering the color. This brought out the detail within the coma. With a stack (aligning on the comet nucleus) of 10, the image stood up well to heavy processing: CCDOPS: range, sRGB+gamma single shot color. Photoshop CS2 and Astronomy Tools v1.4: 3x 'make stars smaller', 'space noise reduction', 'deep space noise reduction', crop, curves, saturation enhance, brightness/contrast, and jpg'd. Jessica will do her own stack, with a much wider array of photos, soon!

Nov 11 - A solo trip under crystal clean post-rain storm skies to Coast Rd again. I was inspired by the pictures showing the bizarre chaotic tails and wanted to capture these myself. However, they're elusive now (or gone?). Or, I need to keep trying different processing. A whole hour I got, so there should be plenty of image depth to plumb. But for now...

Nov 11 ~11pm. 12x5min stack on the nucleus of the comet, in Registax 4. CCDOPS5: sRGB+gamma, no range adjust. Registax 4: stack on nucleus. Photoshop CS2: levels, smart sharpen, saturation enhance, AstronomyTools: 'make stars smaller', 2x 'space noise reduction'. Goal was to bring out the faint outer parts and the way the green C2 emission faded into the yellow dust cloud to make a brown rim on the tail side. No cropping.

Same image, further processed to bring out the faint multiple hoods, and the spiked inner tail. Photoshopc CS2 curves, saturation, AstronomyTools 3x 'local contrast enhance'. No cropping. There's a horizontal discontinuity artifact in the upper part of the coma. Not sure why that happened. All images were tracking well.

Nov 14 - Astrophotography class at the Observatory. I helped Pearl and Kevin each get 3 images of the comet. I've stacked and processed them all 6 together here.

Nov 14 9pm. 6x5min stack in Registax 3. sRGB+gamma single-shot color processing. Photoshop CS2 to bring out the green C2 molecular emission tail. No cropping

Same image stack, Photoshop'ed to bring out inner tail spikes. But notice the boxy demarcation above and also right of the nucleus. This is clearly an artifact. I used Astronomy Tools 'local contrast enhance' a half dozen times to show the tail, but this artifact is clear on other images if you look. I tried this same process on other extended objects like the Orion Nebula from a couple years ago - it's not there. Has our ST2000xcm chip developed a pathology??


Nov 27 - On campus at Cabrillo Observatory. The comet is getting too large to photograph with the 8" f/4 so this night I used the 100mm Zuiko lens. Unfortunately, the lens does not seem to be perfectly planar with the chip, as one side shows noticable blooming of the stars. Also, this setup really needs a good flat field. After taking the image set below, I set up for flat fields using the suspended gray sheet. However, the gray sheet seems no longer to be perfectly flat. I averaged 3 different aimings and the result isn't too bad. However, a better set would include median's to eliminate the transient hot pixels

Nov 27 7:30pm 6x5min stack under good dry moonless conditions, w/ 100mm Zuiko at f/4. Flat fielded and sRGB+gamma color. Stacked in Registax 4 on the stars, Photoshop CS2: 'make stars smaller', 'space noise redux', 'deep space noise redux', 'local contrast enhance', levels, unsharp mask, saturation, cropped slightly.

Dec 12 9:45pm Single 5min shot with the 8" f/4 LXD75, from Cabrillo Observatory. Quite a nice image! Note the tiny image of the barred spiral galaxy NCG 1169 below/right of the nucleus.


Jan 13, '08 1:45am. Same night at Oak Ridge Observatory. I discovered my IR/UV filter would screw into more than just the nosepiece; it'll screw into the recessed chip coverplate, allowing me to use it on any setup. I got just a 2 x 2min grab shots before the comet set over the SF-light polluted northwest between two trees. Most stars are now quite tight, but the brighter ones show imperfect UV and/or IR blocking it would seem.


March 1; Comet Holmes & The California Nebula. 9x5min dark subtracted, flat fielded in CCDOPS5, stacked in Registax 4. Photoshop CS2/Astronomy Tools: cropped, levels, 'enhance DSO/reduce stars', 2x 'make stars smaller', curves, 'space noise reduction', 'deep space noise reduction', 'local contrast enhance'.

March 4. from Cabrillo Observatory, with some cirrus and possible fogging due to dessicant losing power. 3x5min dark, flat corrected in CCDOPS5, stacked in Registax 3, and Photoshop CS2: color balanced, cropped, levels, 'make stars smaller', 'space noise reduction', 'deep space noise reduction', 'local contrast enhance'.

Mar 8, from Bonny Doon. 10x10min dark subtract, flatfield. Stacked in Registax 4. Photoshop CS2: curves, levels, cropped, color balance, 2x 'make stars smaller', 2x 'reduce space noise', 2x 'local contrast enhance', unsharp mask, Some occassional cirrus.